What exactly is protected under this patent US 20130001878A1. I have built a similar product but it's fill mechanism is automatic in nature.
Any patent protects what is listed in the claims -- no more -- no less.
The best way to start is to compare "Claim 1" word-for-word and see if your product matches the description -- if your product differs in just one matter of what is described in the first claim, then it is likely not covered.
Also, making something "automatic" could be an innovative enhancement and patentable in it's own right.
Patent granted on application covers
A target game with a fluid indicator, comprising: a container capable of containing a fluid indicator; the container having a top and a bottom; the top of the container oriented above the bottom of the container; the container assembled below a horizontal bar; the bottom of the container having a fluid indicator escape opening; an actuation housing assembled with the horizontal support bar; the actuation housing having a top vertical opening, a bottom vertical opening, a left horizontal opening, and a right horizontal opening; the bottom vertical opening located inside the container; an actuation rod passing through the top vertical opening and emerging from the bottom vertical opening; the actuation rod having a cap on an end emerging from the top vertical opening; the actuation rod assembled with a spring; the actuation rod having a valve on an end emerging from the bottom vertical opening and the valve suspended inside of the container; the valve removably engaging with the fluid indicator escape opening; the valve moving between an engaged position and a disengaged position; wherein in the engaged position, the valve obstructs the fluid indicator escape opening; and wherein in the disengaged position, the valve unobstructs the fluid indicator escape opening; a swing arm assembled above the actuation housing and applying pressure to the cap; the swing arm connected to a target; such that when the target is struck by a projectile, the swing arm releases the applied pressure on the cap causing the spring to release potential energy and disengaging the valve from the fluid indicator escape opening.
hope it helps.