Hi Mike, and welcome to the site. On all the tanks, be sure that the drain end is the lowest, and I put an additional drain on the low end and a cleanout on the opposite end on the top to facilitate cleaning (especially on the grey and black tanks.
I've been building our own conversion, so I've researced a bunch of parts and materials suppliers, so if i can be of any hepl don't hesitate to let me know. This site is full of lots of people who are building their own and have done their own modifications; whatever your question, someone has been there and done that! I sure have gotten some good advice here.....