How many gallons is an RV holding tank?

There is no single RV holding tank size. Verified listings on this store show examples from 6 gallons to 150 gallons; common replacement sizes include 24, 42, and 53 gallons. Match the old tank's capacity, outside dimensions, drain position, fitting layout, and available clearance before ordering. Gallon capacity by itself does not confirm fitment.

RV holding tank sizes at a glance

The table below uses live product listings and their published part references. Open the product listing for the complete fitting and drain details, and measure your installation space before choosing a replacement.

Capacity	Published dimensions (L × W × H)	Maker / model	Part or SKU reference	Product
6 gal	28 × 17.5 × 6.625 in.	Alpha 211BLANK	211BLANK	View 6-gallon tank
24 gal	70 × 21 × 6 in.	Elkhart RV Parts	4283 / ERV121100	View 24-gallon tank
42 gal	56 × 24.5 × 7 in.	Elkhart Plastics / Ameri-Kart	EPI 4451 / H1248; SKU H1248005/4451	View 42-gallon tank
53 gal	28 × 26 × 22.5 in.	Elkhart Plastics	EPI 9556H / H1301003 / ERV1277; SKU MRM-9556H	View 53-gallon tank
150 gal	71.5 × 66 × 8 in.	ICON WT4014	WT4014; SKU 15198	View 150-gallon tank

What size holding tank do I need?

Choose the replacement by the space and plumbing layout first, then compare capacity. Before ordering, record the old tank's length, width, and height; photograph the tank label and every fitting; and note whether the drain is at the center, end, side, or another position. Also check clearance around frame rails, straps, vents, sensors, and the removal path.

• Small or space-limited installation: compare compact listings such as the 6-gallon Alpha 211BLANK, but confirm its 28 × 17.5 × 6.625-inch footprint and black-water listing details match your setup.
• Mid-size replacement: the 42-gallon EPI 4451 / H1248 is listed at 56 × 24.5 × 7 inches with a center-end drain. Verify that drain position and the product page's complete specifications against the original.
• Taller tank compartment: the 53-gallon EPI 9556H / H1301003 listing is 28 × 26 × 22.5 inches. Do not substitute it for a low-profile tank without checking height and connections.
• Large custom or full-time installation: the ICON WT4014 is listed at 150 gallons and 71.5 × 66 × 8 inches with a 3-inch raised FPT drain. Confirm the footprint and drain configuration before considering it.

Black water vs. gray water holding tanks

Black water tanks collect toilet waste. Gray water tanks collect wastewater from sinks and showers. Some product listings describe a tank for black or gray water applications, while others identify a specific configuration. Treat the product's published description and fitting layout as the source of truth for that listing; do not assume that similarly sized tanks are interchangeable.

How to match a replacement RV holding tank

1. Measure the old tank and opening. Use the same orientation for length, width, and height, and allow for the tank wall, fittings, straps, and removal clearance.
2. Map every connection. Record drain, outlet, fill, vent, and sensor locations. A tank with the wrong outlet position can fail even when the gallon number looks right.
3. Search every identifier. Compare the molded label, OEM reference, model number, SKU, and any EPI, H-series, ERV, Alpha, or ICON number shown on the listing.
4. Confirm what is included. Check whether the listing specifies a fitting, drain, sensor, valve, or tank-only configuration. Do not assume accessories are included.
5. Ask before ordering when uncertain. Send photos, measurements, and the old part number to help@elkhartrvparts.com or call 574-675-6919.

Browse related RV tank resources

Compare the full RV holding tank collection, use the RV Tank Finder when you are shopping by measurements, or see holding tank replacement parts and fittings when the tank needs new connections.

Frequently asked questions

What is the most common RV holding tank size?

There is no universal size. The correct replacement is the one whose capacity, dimensions, drain and fitting layout, and clearance match the original installation. The live examples above include 24, 42, and 53 gallons, among other sizes.

Can I replace a 42-gallon tank with a 53-gallon tank?

Only if the 53-gallon listing's dimensions, connections, drain position, mounting and clearance work in your RV. Compare the published 42-gallon 56 × 24.5 × 7-inch footprint with the 53-gallon 28 × 26 × 22.5-inch footprint; these are materially different shapes.

Do black and gray water tanks use the same size?

They can have similar capacities, but capacity alone does not establish compatibility. Match the original tank's intended use, openings, fittings, drain layout, and dimensions to the replacement listing.

What should I measure before ordering?

Measure length, width, height, every opening and fitting location, drain position, and clearance around the tank. Photograph the label and the plumbing connections so the part reference and layout can be checked together.

Need help matching a tank? Call 574-675-6919 or email help@elkhartrvparts.com with your measurements and photos before ordering.