ProTip: Using Dome Caps inside of Fittings

How to Use Dome Caps to Block PVC Fitting Sockets

We’re often asked if Internal Dome Caps can be used to block the socket or port of a PVC fitting. While it seems straightforward, inserting the cap directly into the socket usually causes it to slip too far inside and wedge unevenly — often at the wrong depth.

The easy fix: add a short piece of PVC pipe into the fitting first. This gives the Dome Cap a secure point of connection, keeping it flush with the socket edge for a smooth, professional finish.

Understanding Insertion Depth

Every PVC fitting has a specific insertion depth — the distance the pipe slides into the socket. FORMUFIT fittings use deeper sockets than plumbing-grade alternatives, so measuring accurately ensures a proper fit.

Here’s the insertion depth chart for FORMUFIT fittings:

*Insertion depth applies to FORMUFIT products only.

Step 1: Cut a Short Pipe Segment

Select the correct pipe size based on your fitting and cut a short piece to the corresponding insertion depth listed above. This short segment acts as the attachment base for your Dome Cap.

Step 2: Attach the Dome Cap

Apply a small amount of PVC cement to the inside of the Dome Cap, then attach it to your pipe segment. Once bonded, insert the pipe-and-cap assembly into the fitting socket and tap gently until seated.

For a permanent seal, apply PVC cement to the outer pipe surface before inserting it into the fitting. This ensures a strong hold and a clean, domed finish at the socket opening.

A Simple, Effective Solution

With just a short piece of PVC pipe, you can easily close off unused sockets in PVC fittings — improving both appearance and functionality. It’s ideal when you want to:

• Close an unused fitting port
• Cap off stubs for a clean finish
• Seal open sockets to prevent debris entry

This simple technique provides a professional, seamless look using parts you already have on hand.