Tank Outlet Sizes: How to Find the Right Tap & Fittings
Not sure which tap, hosetail or valve fits your tank? You only need to know two things: the size of the outlet, and whether its thread is male or female. This guide shows you how to check both in a couple of minutes.
Step 1: Is your outlet male or female?
Look at the outlet on your tank. The thread is either on the outside or the inside, and that decides which fittings will screw onto it.
Male outlet
The outlet sticks out from the tank with the thread on the outside. A tap or fitting with a female thread screws over it.
Most Enduramaxx tanks have a male outlet, with the size chosen when you order.
Female outlet
The outlet is a socket with the thread on the inside. A tap or fitting with a male thread screws into it.
Most Wydale tanks have a female outlet, most commonly ¾” BSP.
Step 2: Measure the thread
Tank outlets in the UK use BSP (British Standard Pipe) threads. The confusing part is that the BSP size is not the size you measure: a ½” BSP thread measures about 21mm across, not 12.7mm. So measure the thread, then use the table below.
- Male outlet: measure across the outside of the thread, from peak to peak.
- Female outlet: measure across the inside of the opening, across the tops of the thread.
A ruler is fine, but a set of callipers gives the best reading. Go with the closest size in the table.
| BSP size | Male thread measures (outside) | Female thread measures (inside) | Fittings |
|---|---|---|---|
| ½” | about 21mm | about 19mm | ½” fittings |
| ¾” | about 26.5mm | about 24mm | ¾” fittings |
| 1″ | about 33mm | about 30mm | 1″ fittings |
| 1¼” | about 42mm | about 39mm | 1¼” fittings |
| 1½” | about 48mm | about 45mm | 1½” fittings |
| 2″ | about 60mm | about 57mm | 2″ fittings |
| 3″ | about 88mm | about 85mm | 3″ and larger |
Bought your tank from us? You may not need to measure at all. The outlet size and thread type are listed on the product page, either in the Product Specification or in the outlet options, and on your order confirmation.
Step 3: Choose your fittings
Once you know the size and thread type, everything in the matching Fittings by Outlet Size section will fit. Here’s what each type is for.
Tap kits
The easiest option. A complete tap kit includes the tap and the fittings to connect it to a set outlet size, so check the kit’s outlet size matches yours.
Taps for drinking water
If the tank holds water for drinking, use a WRAS approved tap. For general use, plastic ball valve taps are a tough, simple choice, and quick release tap kits make it easy to connect and disconnect a hose.
Hosetails
A hosetail lets you run a hose straight from the outlet. You need two sizes: the BSP size of your outlet, and the inside diameter of your hose (for example 12mm, 20mm or 25mm).
Adaptors, reducers and plugs
If the tap or fitting you want is a different size from your outlet, an adaptor or reducer bridges the gap. To blank off an outlet you’re not using, fit a plug.
Fitting tips
- Wrap PTFE tape around male threads before fitting, in the direction the fitting tightens.
- Hand tight plus a little more is plenty. Over-tightening a fitting on a plastic outlet is one of the most common causes of cracks: see our note on avoiding cracked water tanks.
- Fitting a tap for the first time? Follow our step-by-step tap installation guide.
- Need an outlet in a different place on the tank? Read can I fit a new outlet to my water tank?
Frequently asked questions
Is ¾” BSP the same as 20mm?
No. The BSP size is a traditional pipe size, not a measurement of the thread. A ¾” BSP thread measures about 26.5mm across the outside. Some hosetails are described as “¾” x 20mm”: that means a ¾” BSP thread on one end and a 20mm hose connection on the other.
Will a tap from a DIY shop fit my tank?
It will if the BSP size and thread type match your outlet. Check both before you buy, as many garden taps are made for wall plates rather than tank outlets.
My outlet has a cap on it. Is that the outlet size?
The cap screws onto or into the outlet, so it has the same BSP size. Take the cap off and measure the outlet thread itself for the most accurate result.
Can I use a different size tap from my outlet?
Yes, with an adaptor or reducer between the two. For example, a 1″ outlet can take a ¾” tap with a 1″ to ¾” reducer.
Still not sure?
Send us the tank model, or a photo of the outlet next to a tape measure, and we’ll tell you exactly which fittings you need.
Call 01308 479960 or get in touch online.