The anti sump valve is a spring loaded one way (non return) valve. You cannot forget it. It forgets itself.
But with all other reasons not to use it, I agree. I had one on the BSA A65 though, some years ago. I have a new oil pump now and still loose some level, but not nearly as much as I used to. The BSA pump is a gear pump, so not comparable with the Triumph.
Ger B 1971 BSA A-65T, nicknamed "De fiets" (the bicycle); 1996 Triumph Trophy 900, nicknamed by SWMBO: "Dat andere ding" (that other thing).
+1 for no real need for one on a Triumph twin. The stock pump has a built-in-anti-wet-sump valve which is effective enough. As mentioned above, if you are getting wet sump, fix the built-in valve. Re-seat if/as necessary.
Loc: Vic. Australia
There are 2 versions of wet-sumping: 1./Oil-drainage from the tank through the FEED PUMP in the normal direction which gradually floods the crankcase WHILE THE BIKE IS STORED,and not running.It may take weeks or months for the crankcase oil level to rise much.It's more likely to happen with a gear pump (Norton,BSA or Triumph Trident).It's almost unheard of in a Triumph twin with a piston pump.
It's not impossible to happen.I noticed it one time (once in more than 40 years),and more than a pint of oil had drained into the crankcase,but it took more than 6 months to happen.I can only presume that the piston was in a position where the supply ports were open,and that there was also a microscopic particle between the check ball and its seat.There was some exhaust smoke for the first few minutes when it started up.It never happened to that bike again.
I tend to agree with Dave Madigan:Although Norton/BSA riders call this "WET-SUMPING",it's not true wet-sumping;it's oil-drainage while parked for an extended time. If a Triumph experiences wet-sumping,it's more likely to be true wet sumping,type two:
2./If the RETURN pump is at fault,it won't pump enough oil out of the crankcase,and the level rises.The crankcase oil level stays too high even when the engine is running. That's normally caused by a slightly bigger particle between the check-ball and seat on the return pump.That particle normally found its way into the pickup tube when the crankcase drain plug was removed.
You don't need to remove the drain plug at oil change time.95% of the oil is in the oil tank.The rest is in the hoses,pump,crankshaft and crankcase.You can pump that "rest" of the oil out the return hose when you start up.Just disconnect the hose at the tank end and run it into a bucket for the 30 seconds.Then re-connect the hose to the tank.