Here's a look at the interior of the boiler. You can see a 3/8 inch SS nipple welded through the side of the keg.
I tried different manifolds and ended with this setup. It's reliable and easy to keep clean. Connected to the nipple is a SS street 90, an elbow with a female on one end and a male on the other.
The bottom of the nipple will lose siphon with one gallon left in the tun. This allows all the hot break and spent hops to stay. I added a 1/2 SS coupling get reach further towards the bottom. Way too much trub was siphoned. Finally I cut the coupling in half. Now it loses siphon at 1/2 gallon. Seems optimum for 10 gallon batches. I've been using a lot of whole leaf hops lately and have had no problems with this set up.