In my forty years in the meat industry I've never had a customer tell me that they were going to buy a cut of beef out of the meat case and take it home to soak in salt water before using it. In the same vein I have never seen a packing house, meat market, or grocery store  that would soak beef trim in salt water before grinding it. Where this theory came from regarding venison and/or why is a mystery to me.
    Blood is in fact a major contributor to the moisture and flavor in meat and replacing it with salt and water does nothing for the end result in my opinion. We never have or will soak venison for extended periods. (Other than in water with baking soda for a gut shot deer.)
    I believe if you double check our website you will find that we never recommend grinding the venison with "fat" of any kind!
    As I have indicated in several previous answers if you want the best venison burger that my family and our customers prefer try this:
Add 25% of the venison weight in lean pork butt (75% lean or better) and 12.5% in lean round Chuck (Approx. 85% lean). Grind it twice through a fine plate.
Do not over trim the venison, it does not have to be solid red meat!
    With your 4# you would use 1# of pork and 1/2# of Ground Chuck.

    Did you know that the boneless shoulder is excellent in the crock pot? Try seasoning it with seasoned salt, pepper, garlic powder, and Accent (MSG.) Put it in the crock pot and cover 1/2 way with water. Cook on low at least 8 hours. (You can add carrots, potatoes, and onion the last few hours.) Add water if needed.

    Another note is that the Top Blade muscle located on the side of the scapula is the second or third most tender muscle on the animal. It's great left whole, sprayed with olive oil, seasoned with Montreal Steak Seasoning and grilled to medium. (150 - 155F)
       
Dave