First off I think connecting any such device directly to the legs and waist is just asking for trouble, as it’s a sure-fire way to cross load your krabs, and also stop any movement by the Silent Partner, which could cause drag - and so lock it up. I use two methods, the first and most simple being to clip it direct to my belay loop, as this allows free movement, and the krabs have less likely hood of becoming cross-loaded. I tend to have two belay loops (the one on my Petzl harness, plus a Yates one threaded on) so I’ve got plenty of room for other stuff (belay device, daisy chains etc).
The way I attach the Silent Partner is with two small screwgates (or one wire gate and a screwgate for speed) and would avoid maillions (good if you’re using a Grigri to solo) as it’s vital you can get in and out of the device quickly (sometimes mid-pitch when you’ve crossed your ropes!). One biner - even a steel one - is one less component in your safety chain, which as it stands only has three! (2 biners on your Silent Partner and one for your back-up knot). Two back to backs screwgates are 100% safe - locked or unlocked, and proof against cross-loading. Also, two biners allow you to take one krab out, half-open the Silent Partner, re-insert the krab into the open section of the clip slot, clip that off to a sling, then remove the second krab and take the Silent Partner off the rope. A silent partner is very easy to drop, and without it you’ll soon realize that a clove hitch far less functional.
The other way you can tie in is to create a higher tie in point between your harness and chest harness, meaning you have less chance of taking a head-first fall. To do this take a length of full strength cord (I used Dyneema, but a bit of skinny rope will do) and create a fig8 knot on a bite through your chest harness (you need to be able to unthread your chest harness from the bite at the end, so don’t tie it through any close loops), leaving a long tail from one side of the knot.
Now take the tail and pass it through your sit harness and back up, rethreading it through the fig8 knot. Now you have a fig8 with two bites on each side, joining sit and waist harness.
Now take the tail - which is coming out of the top side of the fig8, and create a small bite by threading it back through the fig8.
You now have a fig8 with 3 bites.
The location of the fig8 and this last loop (this is where you’ll clip your Silent Partner, needs to be around your belly button, so as to avoid the Silent Partner smashing you in the face.
Although this knot adds more bulk it lifts the Silent Partner out from between your legs and makes it more visible and less likely to get cluttered up (one advantage of the Silent Partner over a Grigri is that it’s almost impossible to get jammed open, and will lock up in any fall).
Hope that’s of some help.