Dump valve set up

[Ben hdi306]

So I fort I'd put a dump valve on the hdi just purely for the sh*ts and giggles but I can't seem to find what vacume pipe I need to T into. I've set up the solenoid system boost in one end but need to do the vacume in the other. I've T'ed into my boost gauge line will that be ok? Will it still show when I'm fully boosting or be less now, also set up the micro switch on the throttle so all I need to sort out is the vacume any idea/pictures people could help me. Thanks in advance. Ben