First it may not be creosote, second the vents have nothing to do with creosote.
Creosote comes from either un-seasoned wood that has resins in it, or from trying to apply too much smoke at one time, (and too much smoke just really sucks so I am not sure that is actually creosote or just too much smoke). Venting can allow smoke out of the chamber to lessen the smoke build up but its much easier to use less to begin with. You can smoke hours, many hours, many many hours in a totally enclosed chamber and unless you use too much smoke (like too many chips or chunks or splits or branches) you will have no problem.
I do not know what bowl you are talking about, if its a drip pan and you think it needs cleaning, hot water, Dawn dishwashing soap and a green scourring pad works best. If its really excessive, use the steam cleaner at the car wash for find a friend with a steam genie.
There is a natural smoke residue left behind when smoking, if that is what you are seeing, I leave it on. You must decide if your smoker to you is an oven or a BBQ pit. I clean my oven, I have not cleaned a pit besides the occassional sand blasting in 50 years. The natural residue builds and helps seal the smoker. I wire bursh the grates.
I am sure you are allowing your fish to sit and mellow a day or two before freezing, if when you taste it, it makes you gag it might be creosote. If the fish is smoked ok, then you just have smoke residue.
Hope that helps you.