I like these.

WORKSHOP Wet/Dry Vacs Vacuum Adapter WS25007A 2-1/2-Inch Universal Wet/Dry Shop Vacuum Adapter Is An Ideal Shop Vacuum Accessory , Black https://www.amazon.com/dp/B00FX2TGNM/ref=cm_sw_r_apan_glt_i_N2EAN72JBZ6ZG2CSCWKR