My preferred method is a little dish soap (or other liquid soap, even baby shampoo) and running water, nothing physically touching the dome interior but the water spray. Fill partway, and agitate and invert and rinse out until sure that both salt crystals and any sand or grit are gone. Then follow with a hot clean water rinse (hot is important) and add a good sized splash of isopropyl alcohol to cut the surface tension, same theory as using it to help dry out your ears between dives, invert and shake it all out and you should have almost no droplets inside. Let dry on a thick folded towel so air can kind of get in and it doesn't 'fog up' much (inside, low humidity, e.g. air conditioned room).
I don't think the alcohol should be able to harm any of the adhesives used in the dome to port attachment, but to be safe I never let that 'sit' inside very long, more just a swish around of about 1 part isopropyl (70% or so from the typical drug store bottle) to 3 parts hot water, then drain.
Any minor residual droplet marks can be gently polished off with a (CLEAN and dry) microfiber cloth, preferably one recently laundered (no fabric softener) if it was ever used during the trip to pick up grit, minor smears of o-ring lube, etc. Goes without saying you wash and thoroughly dry your hands too before sticking one inside the port ring with the microfiber.
Edited by rtrski, 05 May 2013 - 06:51 AM.
Current rig: Sony SLT-alpha55 in Ikelite housing, Sigma 105mm f2.8 DC Macro w/ Ike 5505.58 flat port or Sigma 8-16mm f/4.5-5.6 DC HSM behind UWCamStuff custom 5" mini-dome. Dual INON z240 Type IVs triggered with DS51 for TTL mimicry, or DS51 alone with home-made ringflash assy for macro.
Topside, unhoused: Sony SLT-alpha99, Sigma 150-500mm + 1.4TC, Sigma 15mm diagonal fish, Sony 24-70mm f2.8 CZ, Tamron 180mm f2.8 Macro...all the gear and nary a clue...