I just called Button Bay State Park because I’m camping in the area next week. They charge to use their dump station if you’re not camping there. Per their website, $25 for RV’s up to 30 feet, $50 for RV’s and buses over 30 feet. (The guy on the phone only said $25 and didn’t mention RV length.)
5 Button Bay State Park Rd, Vergennes, VT 05491
Call for hours: (802) 475-2377
https://www.vtstateparks.com/parks/button-bay
FYI, I haven’t been there. For $25, I probably won’t go.
Vermont
Montpelier Vermont dump station
A $5 (or maybe by donation) dump station is available at the Montpelier wastewater treatment plant, 949 Dog River Rd, Montpelier, VT 05602. It’s less than a mile off/on I89. It’s located on the plant’s north side, nearly across from Montpelier Junction Road.
Rutland, Vermont
Wastewater treatment plant at West St (US-4 Bus) and Greens Hill Ln. 802-773-1863. Free.
Last updated: 8/22/2007
Newport, Vermont
Newport Wastewater Treatment Plant, 94 T P Ln, Newport VT 05855 / 802-334-2124. Free.
Last updated: 12/22/2015
Hartford, Vermont
Quechee State Park, 5800 Woodstock Rd, Hartford VT 05047 / 802-295-2990. Open mid-May to mid-October. Rinse water. $30 or less.
Last updated: 10/4/2019
Fair Haven, Vermont
Exit 1 RV, 1210 Prospect St, Fair Haven VT 05743 / 802-265-3400. Rinse water. $10 or less.
Last updated: 9/23/2019
Bennington, Vermont
Woodford State Park, 142 State Park Rd, Bennington VT 05201 / 802-447-7169. $30 or less.
Last updated: 3/18/2019