# A Cracked Gray Tank and a Wet Underbelly: Tracing RV Plumbing Leaks to the Source

Canonical: https://theocrv.com/blog/tracing-an-rv-plumbing-leak-to-the-source/
Business: OCRV Center, Yorba Linda, CA. Serving Mission Viejo, California.
Phone: (949) 799-3387 | Email: info@ocrvcenter.com

Category: RV, Camper, and Fifth Wheel Repair Tips | Published: 2025-11-24

A wet, sagging, or dripping underbelly almost always means a plumbing leak sitting above it, and the usual suspects are a cracked holding tank, a loosened fitting, or a split supply line. Finding which one means opening the belly wrap and testing each source, because the drip point is rarely where the leak actually starts.

## Why does the underbelly get wet in the first place?

The coroplast or fabric underbelly catches whatever leaks from the plumbing above it. Water pools there, sags the material, and finds the lowest point to drip from, which is often nowhere near the real leak.

## What are the common sources?

- A cracked gray or black holding tank, often from a hard freeze or a strap
- A loose or failed fitting at a tank or pump connection
- A split supply line behind a wall or under the floor
- A leaking low-point drain or valve left weeping
- A city-water inlet or water-heater fitting seeping slowly

## Why not just seal the drip you can see?

The drip is the exit, not the entrance. Sealing the belly there traps water against the floor and framing, and the leak keeps running behind it.
You have to open the belly, dry it out, and pressure-check the system to find the actual source.

## What damage does a slow plumbing leak cause?

Left alone, it soaks insulation, rots the subfloor, and can reach the framing. A cracked tank ignored for a season often turns into floor work, which costs far more than the tank.

## When is this a shop job?

Dropping a full holding tank, chasing a line inside a wall, or repairing a soaked subfloor is shop work. If the belly is sagging or the floor feels soft near a wet spot, that is the signal to bring it in.
> A wet underbelly is a plumbing problem with a floor problem waiting behind it. OCRV Center opens, tests, and repairs RV plumbing at our Yorba Linda facility, and Mission Viejo owners drive up before a cracked tank turns into a rotted floor.