As far as I can remember you must only fit a Drain orf on the lowest point of your rising main, Cannae remember the regs saying you HAVE to fit em anywhere else.
IMHO, it isn't good practise at all - it's a waste of brass, of time and of money, providing nothing more than yet another valve that will eventually leak from its gland.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local