If you bought what I think you bought and are calling it a "winterization kit" then it's not what you need to pull antifreeze from a gallon jug into the FloJet pumphead. I think you bought one of the $20 kits with a couple pieces of short tubing and a 3 way valve ??? If so, it won't work well with your pump.
All you need is a "snap lock pump connector" (about $5 at any RV parts store) and a 3' length of clear (so you can see the antifreeze) vinyl tubing from any big box home store.
This is a link to the connector you need and a photo of it. The vinyl hose is sized to fit the barbed end of the connector. https://www.amazon.com/Flojet-Port-D...gateway&sr=8-1
Just pull the blue tab on the pump inlet side (under the wires in your photo) insert the "vinyl hose/connector" into the hole and push the blue tab closed to lock your "winterization adapter". Turn on the pump and watch the pink stuff flow. When you're done, pull the blue tab, remove the hose and reinstall your existing connector.
As a note, there is no strainer on your pump inlet. You may want to consider protecting your pump and plumbing system by installing a FloJet strainer. You can simply install it at the pump inlet and then install your fresh water tank inlet to the strainer. Here's a photo of the strainer and a link for it as well. Cost for the strainer is around $10. https://www.amazon.com/Flojet-017403...gateway&sr=8-3