Homebrew PCBs

Hi!

I'm thinking about my etch tank.
Even if i make a vertical tank how can i make a airtight lid?
I want to keep the etchant in and prevent too much corrosion.

The lid shoud keep all gases in.
it should have a overpressure valve (because of decomposing H2O2, that is 
no problem).

Additionally it should prevent spattering.
(when the tiny bubbles (from the h2o2) burst there is etchant splattered 
out of the tank.)

The lid ideally should be constructed in a way ensuring any condensed (or 
accumulated from splattering) drops
building up will run down in the tank again, and not run off to the side 
when i take the lid off.

Now to the problem:

How can i ensure a airtight seal if i make the tank myself.
even if i use silicone to make something like a seal?
Would it work to bend the top of the tank outward to make something like a 
flange?
and on that a bead of silicone (nice flat) as a seal?
How to press the lid (with the pcb holder) against it?


The other idea: (horizontal etch tank)
Take a big tupperware container.
(the seals of these containers are tight enough for me i think.)
fill it a inch or so with etchant.
now suspend the pcb (somehow) in mid-etchant.
some holding mechainsm on the lid is needed again.


The whole jar can be mounted to a heavy wood plate, just to make it harder 
to knock it over
while removing the lid.


While etching the lid may only rest loosely on the cointainer, this would 
be enough to catch the splattes.
To store it away just press on the lid.

Two questions bother me to this idea:

a)is the lid really tight enough
b)is it a problem to etch horizontally (for uniformity?)
in tray etching the edges are faster, but it doesn't cause trouble.
i nudge the jar sometimes to mix the etchant.

I don't really like the idea of a bubbler but mechanic agitation is ok.
(it might be enough to slightly press on the lid of the tupperware 
container a few times
to make the etchant mix? assume the pcb is hold to the lid and acts as a 
stirring paddle)


Let me know what you think of the idea.


Stefan