If your tubs been fine to this point yes draining is required. But a flush of the pipes may not be necessary. Super chlorinate, drain, start again, no worry's. You could make people shower all the gunk (makeup,soap,hair products,body lotions, body oils, laundry soap in the suits,others) But it will still take some TLC after a party. Only you control how people use your tub. But you don't want to be a spa nazi. Or maybe you do? Plan your party's around water changes? There's lots of little tricks. I like fresh water so if it's within a month or so of normal drain, party on, drain extra. You bought the tub to enjoy, enjoy.