For that steam cleaner, a pressure cooker would save you a lot of fiddling around with a spout. If you don’t have one now, they have a nice nipple on the lid, probably 1/4″ OD.
I’m figuring on using the guns I have now for BP. 38sp, 357, 9mm, 40 S&W and bolt guns. Thet will uave a reduced velocity but I can make accommodation.