Don't understand the oil and water bit, Tap & Spile Fridays is a mixed session and I think it works quite well for all, I have it on good authority that should one sing on tuesday nights session at the Maltings one is thrown out by the management, the session musicians are not so bothered, and, sundays at the Golden Ball have a bit of singing mmmmmmm and yet alas I did once, at the Traf Bay, threaten to drive a fiddlers bow up his a**e if he didn't take a break and give the voices a chance but that is pretty rare these days.
Peter