I really like the Sequence pumps.

You've definitely done some homework.

Yes you can run both skimmer and bottom drain off of the same pump, But I would use a WYE, and a long turn one at that. Also put a Knife valve on each leg, so you can adjust the suck. Many people just use the bottom drain once a week/month, as if the skimmer is working well, there is less debris for the bottom drain to pick up.

I would consider, just personal preference, adding a submersible pump to the skimmer, so that during the fall/spring, you can run just the skimmer, before it's warm enough to run the Ultima.

Sounds like a nice system.

Greg

Sequence pumps are good and so are W Lim pumps.

I have Bottom drains and 55 gallon barrels for my filtration system. I clean the filters once a week and net the tads and fish fry that make the trip through the BD. This works for me. I had one fish that I would remove every week from the filter. He seemed to like the ride.LOL

This is our Sequence 4200PRM15 pump, with Ultima II 4000 filter, and 40 watt Aqua Ultraviolet. We have a 3" Tetra bottom drain.

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Our pond:
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pumphouse:
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Bottom drains are only a bad idea for small fish and tadpoles if your drains are piped directly to a pump. If your drain goes to a settling tank first, then there is no problem because the fish and taddies will be safe sitting in the settling tank until you come along to rescue them. I like sequence pumps....but I do prefer W. Lim pumps. They are more expensive, but they are VERY efficient and well designed and also VERY quiet! I accidently ran one of my Lim pumps for around 20 hours with no water in it and it didn't hurt it a bit!!

Here's a link to a DIY filter I built a couple of weeks ago. I am VERY happy with the performance of this filter!

Here is a link that might be useful: DIY filter