Re: Question about Tubs
That's a compromise. If you want or need to compromise, then a tunnel to another tub is better than nothing. I recommend just cutting down the middle of both sides and creating a minimum 8" walkway between cages. Put something under the gap to prevent bedding spillage.
The best solution is toss the tubs. Spend the time and effort to find a sheet of Coroplast and make one larger space. $10 to $20. About the same as the price of two tubs or less.
Also, the tub shouldn't be much over 10" high. And it should be pretty big to start with.