The Cylon Class Tanker is one constant with the Cylons, regardless of what they do, and how they progress, they need fuel, for their ships, and ultimately for themselves one supposes.
As such, they have two types of the tanker that they use - the armed and unarmed types, and many variants.

Regardless of which version they use, the Cylon Class tanker itself is a woefully unremarkable ship, having either none or very little in the way of defensive weaponry, and the only redeeming feature is that the tanker itself actually carries a flight of Raider fighters with which to defend itself against small aggressors, such as pirates.

They are, and have always been, prime targets for Colonial forces who seek to destroy them at any opportunity given, although with the destruction of the Colonies the objective has been to capture them for the fuel they hold.

Variants:

The Cylons do use several variants of the versatile tanker craft.

Cargo Carrier

This is an externally similar variant to the tanker, but instead of carrying liquid stores, it carries solid materials.

Fighter-less

This version of the tanker simply removes the fighter flight. In its place, the ship carries more fuel.

Fighter Carrier

A rare variant of the tanker, this model sacrifices most of its cargo carrying ability to be able to carry more fighters. Sometimes used as a long-range strike carry as the fuel carried allows for a much-extended range for the tanker and the Raiders carried. It is recognisable from the basic model in that the cargo section is much smaller and the shuttle bay much larger. It is always armed.

Power Ship

Another rare ship, the power ship is a tanker variant which strips out all the fuel capacity of the ship and replaces it with heavy duty power generators and the means to beam this power to other ships. The Cylons have little use for such a ship as their capital ships can generally generate all the power that they and their ambush screens need, but sometimes these ships can be found escorting small convoys of ships which do not have the ability to generate ambush fields. For some reason, these ships are almost never armed, relying on their fighters for protection.

Q-Tanker

A rare variant is the Q-Tanker. To all appearances, the Q-tanker appears like an ordinary tanker, but its job is not to carry cargo. Instead, this variant carries additional fighters and weaponary. It acts like a normal tanker, and sometimes travels with a tanker convoy, but when it is attacked, the ship suddenly sprouts additional gun turrets and additional fighters and gets into the thick of things. As stated, the Q-tanker is quite a rare ship, generally because tanker convoys are usually escorted by heavy capital ships and thus have no need of extra firepower, but they are sometimes seen on the edges of Cylon space as tempting targets for small groups of fighters or pirates.

SSD's designed and drawn by me.

Tankers have one shuttle bay. The bay has one launch tube [J1.54] which will propel a fighter flight to speed 12 and will launch in direction 1) and the equivalent of a standard shuttle hatch (launching and landing from any direction).
The shuttle bay is not large enough to accept yachts.
Tankers have a hyperspeed multiplier of x1.

Cylon Cylon Class Tanker boarding diagram:

Tankers should be represented by the normal Small Freighter Boarding Diagram.

Master Ship Chart Extract:

Annex #7B: Ships able to land on planets

These ships may land on a planet via Powered landings (P2.434).

Annex #7G: Carrier information & Annex #7N: Missile reloads