Water Vac and Ich

We use the large vacuum for both the 55g and the 220g. Because we have been using this vacuum to do the wc's on the 220g (which is undergoing an ich breakout), can we still use it to change the water in the 55g if we run lots of hot water through it beforehand? I want to be as safe as possible, so if it means using our small manual vac that we use on the 5.5g, we'll do that instead (it will take a lot longer using this thing on the 55g, but well worth it if it is safer).

Also, if it is not safe to use the big vac, I assume that it will be okay to use it again after this disease runs it course? I'm wouldn't look forward to opening the wallet for another expensive vac, but, of course, in the end, I'd completely empty my wallet for the health of my fish, without question! So, if it is safer to buy an addiotnal vac for the 55 - I'm onboard.

I've always sterilized the gravel vac and nets with a bleach solution when dealing with an outbreak of ich to avoid transfer between tanks. (Remember to rinse thoroughly to remove any traces of bleach).

So, where this is a pressure vac, if we were to go this route, would we fill a bucket with a small amount of bleach and water and then siphon it out into the sink, and then run hot water through in the opposite direction to rinse out the bleach (and if so, how long should we let the hot water to run through to ensure it is safe for the fish?)? It makes me feel very nervouse using bleach