How to Repair a Hole in RV Grey Water Tank

The Rundown

Your approach is absolutely correct for fixing that 1-inch hole in your ABS gray tank. The patch-and-fiberglass method you've outlined will create a permanent, leak-proof repair that's actually stronger than the original tank material. Your decision to remove the tank from that cramped rear wheel vault was smart - trying to work in that torture position with all those metal bars would have been a nightmare and likely resulted in a poor repair. The fact that your drain pipe "disappeared" during removal is frustrating but common when tanks have been in service for years and connections have settled or shifted.

ABS plastic is indeed fortunate for repairs compared to polyethylene tanks. Your heat-forming technique for the patch piece and surface preparation with beveled edges and scuffing shows you understand the critical factors for a strong bond. The combination of ABS cement followed by fiberglass reinforcement will give you a repair that can easily last another decade or more.

Why It Happens

Drilling mishaps like yours happen more often than RV owners admit, especially when running new cables or installing equipment in tight spaces. The rear wheel vault area is particularly treacherous because it looks spacious from the outside, but once you're working inside with all those frame rails and cross-members, depth perception gets thrown off. Many techs have been there - what looks like plenty of clearance suddenly isn't when you're committed to the drill bit.

The "disappearing" drain pipe situation you experienced occurs because RV manufacturers often use flexible connections that can shift over time, or the pipe may have been barely held in place by the tank's weight and position. When tanks are removed after years of service, these connections can literally fall away into wall cavities or drop down behind other components. It's one of those Murphy's Law moments that makes a simple tank repair turn into a treasure hunt.

Gather These Items

For your ABS tank repair, you'll need ABS cement (not PVC cement - they're different), a piece of ABS pipe or ABS sheet material for the patch, and fine-grit sandpaper or a sanding block. Get some acetone or ABS cleaner for surface preparation, along with disposable gloves and good ventilation. The ABS cement creates toxic fumes and bonds instantly, so work carefully. Ensure adequate ventilation and consider respiratory protection, especially during the extended epoxy fiberglass work.

For the fiberglass reinforcement layer, grab some fiberglass cloth (not mat - cloth conforms better to curves), epoxy resin, hardener, mixing cups, and disposable brushes. You'll also want some plastic sheeting to protect surrounding areas and maybe some cardboard to create a backing if you need to work from both sides. A heat gun will help with your patch forming, and having some clamps or weights ready will help hold everything in position during curing.

The Fix

Start by thoroughly cleaning both the hole area and your pre-formed patch with acetone, then scuff both surfaces with 80-100 grit sandpaper. The mechanical bond from scuffing is crucial for ABS cement to work properly. Test-fit your patch first - it should overlap the hole by at least 1/2 inch on all sides. Apply ABS cement to both surfaces quickly and press the patch into place immediately. You have about 10-15 seconds of working time before the cement starts to set, so practice the motion first.

Once the ABS patch has cured for at least 1-2 hours, prepare your fiberglass reinforcement. Cut your cloth to extend 2-3 inches beyond the patch in all directions. Mix only small batches of epoxy at a time and apply it in thin, even coats. Work out any air bubbles with a brush or squeegee. Apply the cloth and saturate it thoroughly with more epoxy, ensuring complete wet-out. Let this cure for 24 hours before handling, then sand smooth and apply a second layer if desired for extra strength.

For that disappearing drain pipe, you'll need to trace where it went and likely install a new connection. This might involve removing interior panels or accessing the area from above. Consider upgrading to a more secure connection method while you're at it - maybe a threaded fitting instead of whatever slip-connection failed you.

Know Your Limits

This repair is well within DIY capabilities, but take your time with each step. ABS cement doesn't give second chances - once you commit the patch, that's it. If you're not confident with the fiberglass work, many auto body shops can help with that portion for $50-100, and they'll have proper spray booth ventilation for the epoxy work.

The tank reinstallation might be where you want professional help, especially dealing with that mystery drain pipe. A mobile RV tech can sort out the plumbing connections properly and ensure everything's sealed and supported correctly. Budget around $200-300 for professional installation if you decide to go that route. Don't rush the curing times - a few extra days waiting beats doing this repair twice.