Drainage installation from the front face of new or existing structures, with no back-side excavation. A field guide for contractors covering unit selection, the install sequence, drain spacing, fabric selection, and maintenance.
Maintainable weep hole filters install through the face of the wall, with no back-side excavation, and the filter stays accessible for cleaning.
That single difference changes how drainage installation and service work in the field. Here is what a contractor needs to put JET Filter™ units in correctly, from picking the right size through spacing, fastening, sealing, and long-term service.
+92%
flow rate vs. 4″ weep hole
2.7x
filter surface area vs. 6″ weep hole
100+ yrs
316L housing service life
~30 sec
to set each unit
Before You Start: Confirm the Right Unit
JET Filter™ comes in three stainless steel sizes: 3 inch, 4 inch, and 6 inch. Every unit pairs a 316L stainless steel housing with a UV protected ABS cartridge and a woven geotextile filter fabric, with Mirafi® Filter-Weave FW 300 as the standard fabric. Five quick confirmations before any drainage installation starts.
Pre-Installation Checklist
Size and model. Pick 3, 4, or 6 inch based on required flow and the spacing in your plans. Bigger units move more water and space farther apart.
Standard or check valve. Use a check valve model (CVLV) for tidal, submerged, or backflow conditions.
Housing. Every standard unit uses a 316L stainless steel housing: the right call for marine, coastal, DOT, and high moisture work, and Buy America compliant.
Filter fabric. Standard woven Mirafi® FW 300, or a special order fabric matched to your backfill (see fabric selection below).
Quantity and layout. Confirm the drain count and spacing from your project drawings before you core.
Tools and Materials
Nothing exotic. Drainage installation runs on standard tools. The Michigan DOT box culvert demonstration used nothing beyond those and the hardware that ships in the box.
- Core drill with a core bit sized to the unit. On the demonstration, a 4 inch bit was centered over the existing 3 inch weep hole during retrofit.
- Hammer drill with a 3/16 inch masonry bit for the mounting pilot holes.
- A nut driver for seating the mounting screws.
- The four 1/4 inch stainless steel concrete screws provided with each unit.
- A ratchet or wrench to finish tightening, without over tightening.
- The flange gasket supplied with the unit.
- Clean drainage stone, for example MDOT 6A, for filling voids in drier retrofit or new construction conditions.
Substrate note: The fastening hardware described here is for concrete. JET Filter™ units also install in steel, vinyl, aluminum, composite sheet pile, MSE, and wood walls. Confirm substrate appropriate fasteners with JET Filter™ before installing in non concrete walls.
Step-by-Step Drainage Installation
This is the drainage installation sequence documented during the Michigan DOT twin box culvert demonstration, including the field adjustments the crew made to keep backfill from running out of the hole.
Installation Sequence
Locate and prepare. Position the unit at the weep hole location. On a retrofit, center the core over the existing weep hole where possible. Existing grout or rubber stoppers do not need to be removed before coring.
Core the hole. Mount the core drill to the wall and core through to the backfill.
Manage saturated backfill. In saturated or liquefied sand, backfill can pour from the cored hole the moment the bit comes out. Unscrew the core bit from the drill and remove the drill from the wall before backing the bit out, so the unit can go in immediately with minimal loss of material.
Set the housing. Place the housing, with the filter cartridge inside, into the cored hole. Orient the unit with the logo at the top and the drip guard pointing straight down.
Mark and drill pilot holes. Using the mounting flange as a template, drill four 3/16 inch pilot holes into the concrete with a hammer drill.
Fasten the unit. Drive the four 1/4 inch stainless steel concrete screws most of the way with a nut driver, then finish with a ratchet or wrench. Do not over tighten. If a screw head shears during tightening, pull the unit, rotate the flange slightly, and drill new pilot holes.
Seal the flange. Confirm the flange gasket seats against a smooth concrete surface for a full perimeter seal. If the concrete below the old weep hole is abraded or deteriorated, offset the new drain left or right to smoother concrete so the gasket seals.
Backfill voids when conditions allow. In drier retrofit conditions or on new construction, fill voids around the cored hole with clean drainage stone. In saturated, permeable sand this step is often skipped, because the saturated material prevents stone placement.
Field tip, the saturated soil sequence: On the demonstration, the first cored hole let go of liquefied sand almost instantly. Pulling the core drill before backing the bit out, with the unit staged and ready, was the one change that cut the backfill loss. Stage every unit before you core.
How Many Filters, and How Far Apart
Spacing is the horizontal distance between drains in a single row along the wall, and it sets how many units a drainage installation needs. Three things drive it: bigger drains relieve pressure over a wider area, so they space farther apart; drains that penetrate the backfill space wider than ones that do not, though thick walls may prevent penetration; and the higher the groundwater sits above the drain, the closer the spacing. The numbers below come from the University of Missouri design guide.
| Drain Size | Maximum Spacing |
|---|---|
| 2.5″ | 8 ft |
| 4″ | 23 ft |
| 6″ | 30 ft |
Example from the University of Missouri Design Guide for Maintainable Drains (2017), for 10 ft of groundwater above the drain where the drain does not penetrate the backfill. The maximum design spacing for any size or groundwater height is 30 ft. The guide lists a 2.5 inch size; the JET Filter™ stainless line uses a 3 inch unit in its place. Use project specific engineering for final spacing.
To lay out a drainage installation: divide the wall length by the design spacing and round up for the number of drains. Divide the wall length by that number for the construction spacing. Center the row so each end of the wall sits half a spacing from the nearest drain. On long walls with variable height, split the wall into segments and space wider where the wall is shorter.
Matching the Filter Fabric to Your Backfill
The cartridge is replaceable, so the geotextile is something you match to the soil, not a fixed feature. The University of Missouri guide uses the AASHTO M 288 subsurface drainage criteria below to balance drainage against soil retention. Match the fabric before the drainage installation starts, not after.
| Backfill Fines (% passing No. 200) | Max Apparent Opening Size | Min Permittivity | Example Woven Fabric |
|---|---|---|---|
| Less than 15% | No. 40 (0.43 mm) | 0.5 sec⁻¹ | Mirafi® FW 400 |
| 15 to 50% | No. 60 (0.25 mm) | 0.2 sec⁻¹ | Per project |
| More than 50% | No. 70 (0.22 mm) | 0.1 sec⁻¹ | Mirafi® FW 700 |
Criteria from AASHTO M 288 as presented in the University of Missouri Design Guide for Maintainable Drains. JET Filter™ units ship with woven Mirafi® Filter-Weave FW 300 as standard; other woven fabrics can be special ordered. For drainage, give preference to permeability and anti clogging. If a fabric meets the permittivity criterion but not the opening size criterion, inspect the drain regularly and step down to a smaller opening size if backfill loss shows up.
Field Time and Cost
Because the units install and are serviced from the exposed face, a retrofit drainage installation never touches the back, earth retained side of the wall. Once the hole is cored, each unit seats and secures in about 30 seconds. On the Michigan DOT box culvert demonstration, the crew put in 52 units in one and a half working days.
52
units installed
1.5
working days
0
back-side digs
Restoring drainage from the front face is documented as a lower cost approach than repairing or replacing weep holes from the back side, which means excavation, time, and disruption.
After Installation: Inspection and Maintenance
Maintenance after a drainage installation is the easy part. Pull the inner cartridge, check the filter fabric, clean or replace it, and reseat it. No housing removal, no excavation, no special tools, and about 5 minutes per unit.
Standard cartridge cleaning intervals are 3 to 5 years for the 3 inch unit, 4 to 7 years for the 4 inch unit, and 6 to 10 years for the 6 inch unit. The 316L stainless steel housing carries a service life of 100 plus years, and the cartridge and face plate can be replaced over that lifespan. Local conditions can shorten cleaning intervals, for example where sediment loads are high. Where iron mineral bacteria produce iron ochre, the demonstration found the buildup rinsed off the filters easily.
JET Filter™ Models
All JET Filter™ stainless steel models use 316L grade housing and are available with a check valve (CVLV) in each size for tidal and backflow applications.
| Model | Size | Flow Rate (2.5 PSI) | vs. Traditional | Surface Area | Maint. Interval |
|---|---|---|---|---|---|
| JF3SS | 3″ | 52.2 GPM | +35% | 17.44 in² (2.47x) | 3–5 Years |
| JF4SS | 4″ | 121.9 GPM | +92% | 26.03 in² (2.07x) | 4–7 Years |
| JF6SS | 6″ | 263.4 GPM | +87% | 76.95 in² (2.72x) | 6–10 Years |
Flow rates measured at 2.5 PSI with no soil resistance, per TRI Environmental Report MAPP-LSH 2020-003. Flow multiplier and surface area shown versus a standard 2D weep hole of the same diameter. Full data at Product Comparison Guide.
Planning a Drainage Installation?
Cut sheets, CAD and STEP files, drainage installation guidance, and project support are available through the Engineering Hub at no cost.
DOT approved. Buy America compliant. US Patents #7,615,148 (open end) and #10,124,281 (check valve).