I haven’t had Soylent yet but it sounds like you are getting dehydrated. Powered type foods have about as much fluid in it as regular meals so they don’t give you enough moisture to sustain you it seems. I believe in the instructions for Soylent recommends for the customer to drink water as they normally should with meals. I think the recommended daily amount is 8 glasses (16 ounces or 2 cups) or more a day.
Try gargling with 1/4 teapoon of salt mixed with 16 ounces of warm water. It can help to break up the mucus. Just be aware that using salt water too often to gargle with can harm the enamel of your teeth so don’t do it all the time.
You can also try a netipot or a Sinupulse.
Important information on how to use a Neti Pot: http://www.forbes.com/sites/daviddisalvo/2012/08/27/how-not-to-die-using-a-neti-pot/
The very first thing when I wake up in the morning is drink 2 glasses of water then I gargle and clean my teeth. All of this can help break up the mucus for the long day.
Also, make sure never to use the above sinus irrigation systems if your nose is stuff. That will only create more pressure and cause infection so only do it when your sinuses are clear and properly as a way to prevent post nasal drip.