It’s best to use slip made with your own clay when connecting attachments. I like my slip to be the consistency of syrup, and use a brush to clean the excess slip away after attaching parts. I used to use the edge of the container to scrape the excess off of the brush, but it would build up on the edge where I rest the brush handle. To avoid the mess, I adapted an ordinary recycled plastic container. I made four little holes in the sides of the container, slid thread through the holes, and tied the ends in a knot (thin wire would work if you are using clay containing iron as rust contamination would not be an issue). Make the thread tight at first. As it soaks in water, it will expand to the perfect length.
These strings allow me to scrape off the excess slip so it drips into the middle of the container (1). The edge of the container remains clean so the handle of the brush won’t get messy, leaving my hands clean and ready to keep working. Resting the brush in the air also prevents it from getting damaged by soaking in slip all the time (2). The clean edge allows for a better seal when I put the lid on the container, which means my slip stays at the ideal consistency longer.