Them are the ones with the two, 2" bungs in them? If your macerating toilet connections are that small, your in luck. If not, read the following.
After mounting your tanks at about 5 degrees of tilt, (toilet fill hole will be the highest point when done) with the existing bungs in a vertical position from each other, mark a spot 6" by 6" half way down the drum at the now top, (was the side). Cut that square out with a saws all. Buy two 3" abs bulkhead fittings. Use the right size hole saw and cut out the top 2 hole. This is where you will install the first 3" bulkhead fitting, and this will be the one you connect the toilet to. At the opposite end ( used to be the bottom of the drum) as close to the bottom as possible while still having room for the Bulkhead fitting, cut one more hole with the hole saw. This will be your drain. Bottom 2" port gets permanently sealed. Tank venting is done either by installing a 1/2 bulkhead fitting, or T off the toilet connection between the toilet and the tank. Now to reseal your access hole, you need to sacrifice one drum to seal the rest. Using a spare drum ( you should have a few at that price) Cut a piece 10" by 10" out of the side with a saws all. This will be your patch for the access hole. Use some nice coarse sand paper and rough up your overlaps. Apply some good silicone, and screw down every 2" to get a good seal. For this you will need some number 10 coarse thread pan head screws.
3" ABS Bulkhead fittings.
Hope this helps.
Nat