I didn't refit one when I did the bulkhead, thinning I'd get loads of drain back and I'd have to activate the pump for a while to get any water (this wasn't intentional, I just didn't have th valve)
Curiously, the performance seems no different to before?
I did, however, change from 300 washer bottle / pump to td5 bottle / pump, so maybe those pumps have them in built or something? But I kind of doubt it.
Maybe just get a joiner (how long are the tails on the valve - maybe you could snip one off and use that?) and see if the performance is as poor as I expected, but did not actually find?